Multicasting provides for efficient point-to-multipoint data communication. In an IP multicasting environment, a single multicast traffic flow originates at a source and is replicated by routers at points where the network paths leading to the ultimate recipients of the multicast traffic diverge. Accordingly, a network link in a distribution tree carrying a multicast traffic flow to multiple user devices need only carry one copy of the multicast traffic flow, thereby conserving core and access network bandwidth, easing the burden on individual routers in the distribution tree, and allowing a greater number of user devices to receive the traffic flow.
IP datagrams corresponding to a multicast traffic flow are addressed to a single IP destination address identifying a multicast group. A user device accesses an IP multicast traffic flow by joining the multicast group associated with the traffic flow. A user device in turn joins a multicast group by submitting an Internet Group Management Protocol (IGMP) join request to the access network providing access to one or more core networks delivering multicast traffic.
A drawback of IGMP is that it does not allow for differentiation among user systems or user devices. As a result, all IGMP join requests are typically granted without deliberation, and any user device may typically join a multicast group. In a resource-constrained network, this may result in over-subscription, which may in turn cause problems, such as packet loss and delay, adversely affecting services provided by the access network. Where IP multicasting is used to deliver video services, such problems can seriously undermine the ability of content providers to deliver high-quality video service. Video services are extremely sensitive to data loss and delay. As result, over-subscription may severely affect the quality of video services delivered using IP multicasting. While Reservation Protocol (RSVP) may solve some of the problems associated with managing IP multicast traffic bandwidth, RSVP is an upper-layer protocol that relies on application programs generating RSVP messages to request bandwidth. Accordingly, RSVP may not be used to prevent over-subscription where multicast groups are joined by clients that are not RSVP-aware. For these and other reasons, traditional IP multicasting may be insufficient for providing video and other services sensitive to data loss and delay.